Submitted to: Society for Range Management Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 2/10/1998
Publication Date: N/A
Technical Abstract: Since the turn of the century, many grasslands in the southwestern United States have been transformed to savannas or shrublands. This change in vegetation has been accomplished by accelerated erosion and loss of the grazing resource. However, the extent and cause remain controversial. A long-term vegetation chronology can provide a perspective for evaluating recent vegetation change, land use, and erosion, as well as insights into climate and atmospheric change. The purpose of this research was to investigate the post-glacial grass-shrub community composition at the Walnut Gulch Experimental Watershed in southeastern Arizona by evaluating the delta carbon-13 signatures of soil organic matter. Plants which photosynthesize via the Calvin cycle (C3) have a distinctly different ratio of carbon-13 to carbon-12 in their tissues than plants which photosynthesize via the Hatch-Slack pathway (C4). On Arizona grasslands, the primary C3 plants are shrubs and the primary C4 species are perennial grasses. The delta carbon-13 of soil organic matter reflects that of the contributing vegetation. Soil profiles were excavated on a tobosa swale and the surrounding creosote and whitethorn dominated hillslopes. The delta carbon-13 values of soil organic matter at various depths were determined by mass spectrometry. The delta carbon-13 signatures for the present plant communities at the soil profile sites were also ascertained.